Euthyroid hyperthyroxinemia and thyroxine-binding prealbumin excess in islet cell carcinoma

2016 American Thyroid Association Guidelines for Diagnosis and Management of Hyperthyroidism and Other Causes of Thyrotoxicosis

BACKGROUND

Thyrotoxicosis has multiple etiologies, manifestations, and potential therapies. Appropriate treatment requires an accurate diagnosis and is influenced by coexisting medical conditions and patient preference. This document describes evidence-based clinical guidelines for the management of thyrotoxicosis that would be useful to generalist and subspecialty physicians and others providing care for patients with this condition.

METHODS

The American Thyroid Association (ATA) previously cosponsored guidelines for the management of thyrotoxicosis that were published in 2011. Considerable new literature has been published since then, and the ATA felt updated evidence-based guidelines were needed. The association assembled a task force of expert clinicians who authored this report. They examined relevant literature using a systematic PubMed search supplemented with additional published materials. An evidence-based medicine approach that incorporated the knowledge and experience of the panel was used to update the 2011 text and recommendations. The strength of the recommendations and the quality of evidence supporting them were rated according to the approach recommended by the Grading of Recommendations, Assessment, Development, and Evaluation Group.

RESULTS

Clinical topics addressed include the initial evaluation and management of thyrotoxicosis; management of Graves' hyperthyroidism using radioactive iodine, antithyroid drugs, or surgery; management of toxic multinodular goiter or toxic adenoma using radioactive iodine or surgery; Graves' disease in children, adolescents, or pregnant patients; subclinical hyperthyroidism; hyperthyroidism in patients with Graves' orbitopathy; and management of other miscellaneous causes of thyrotoxicosis. New paradigms since publication of the 2011 guidelines are presented for the evaluation of the etiology of thyrotoxicosis, the management of Graves' hyperthyroidism with antithyroid drugs, the management of pregnant hyperthyroid patients, and the preparation of patients for thyroid surgery. The sections on less common causes of thyrotoxicosis have been expanded.

CONCLUSIONS

One hundred twenty-four evidence-based recommendations were developed to aid in the care of patients with thyrotoxicosis and to share what the task force believes is current, rational, and optimal medical practice.

The Brazilian consensus for the diagnosis and treatment of hyperthyroidism: recommendations by the Thyroid Department of the Brazilian Society of Endocrinology and Metabolism

INTRODUCTION

Hyperthyroidism is characterized by increased synthesis and release of thyroid hormones by the thyroid gland. Thyrotoxicosis refers to the clinical syndrome resulting from excessive circulating thyroid hormones, secondary to hyperthyroidism or due to other causes. This article describes evidence-based guidelines for the clinical management of thyrotoxicosis.

OBJECTIVE

This consensus, developed by Brazilian experts and sponsored by the Department of Thyroid Brazilian Society of Endocrinology and Metabolism, aims to address the management, diagnosis and treatment of patients with thyrotoxicosis, according to the most recent evidence from the literature and appropriate for the clinical reality of Brazil.

MATERIALS AND METHODS

After structuring clinical questions, search for evidence was made available in the literature, initially in the database MedLine, PubMed and Embase databases and subsequently in SciELO - Lilacs. The strength of evidence was evaluated by Oxford classification system was established from the study design used, considering the best available evidence for each question.

RESULTS

We have defined 13 questions about the initial clinical approach for the diagnosis and treatment that resulted in 53 recommendations, including the etiology, treatment with antithyroid drugs, radioactive iodine and surgery. We also addressed hyperthyroidism in children, teenagers or pregnant patients, and management of hyperthyroidism in patients with Graves' ophthalmopathy and various other causes of thyrotoxicosis.

CONCLUSIONS

The clinical diagnosis of hyperthyroidism usually offers no difficulty and should be made with measurements of serum TSH and thyroid hormones. The treatment can be performed with antithyroid drugs, surgery or administration of radioactive iodine according to the etiology of thyrotoxicosis, local availability of methods and preferences of the attending physician and patient.

The diagnosis and management of hyperthyroidism in Korea: consensus report of the korean thyroid association

Hyperthyroidism is one of the causes of thyrotoxicosis and the most common cause of hyperthyroidism in Korea is Graves disease. The diagnosis and treatment of Graves disease are different according to geographical area. Recently, the American Thyroid Association and the American Association of Clinical Endocrinologists suggested new management guidelines for hyperthyroidism. However, these guidelines are different from clinical practice in Korea and are difficult to apply. Therefore, the Korean Thyroid Association (KTA) conducted a survey of KTA members regarding the diagnosis and treatment of hyperthyroidism, and reported the consensus on the management of hyperthyroidism. In this review, we summarized the KTA report on the contemporary practice patterns in the diagnosis and management of hyperthyroidism, and compared this report with guidelines from other countries.

Hyperthyroidism and other causes of thyrotoxicosis: management guidelines of the American Thyroid Association and American Association of Clinical Endocrinologists

OBJECTIVE

Thyrotoxicosis has multiple etiologies, manifestations, and potential therapies. Appropriate treatment requires an accurate diagnosis and is influenced by coexisting medical conditions and patient preference. This article describes evidence-based clinical guidelines for the management of thyrotoxicosis that would be useful to generalist and subspeciality physicians and others providing care for patients with this condition.

METHODS

The development of these guidelines was commissioned by the American Thyroid Association in association with the American Association of Clinical Endocrinologists. The American Thyroid Association and American Association of Clinical Endocrinologists assembled a task force of expert clinicians who authored this report. The task force examined relevant literature using a systematic PubMed search supplemented with additional published materials. An evidence-based medicine approach that incorporated the knowledge and experience of the panel was used to develop the text and a series of specific recommendations. The strength of the recommendations and the quality of evidence supporting each was rated according to the approach recommended by the Grading of Recommendations, Assessment, Development, and Evaluation Group.

RESULTS

Clinical topics addressed include the initial evaluation and management of thyrotoxicosis; management of Graves' hyperthyroidism using radioactive iodine, antithyroid drugs, or surgery; management of toxic multinodular goiter or toxic adenoma using radioactive iodine or surgery; Graves' disease in children, adolescents, or pregnant patients; subclinical hyperthyroidism; hyperthyroidism in patients with Graves' ophthalmopathy; and management of other miscellaneous causes of thyrotoxicosis.

CONCLUSIONS

One hundred evidence-based recommendations were developed to aid in the care of patients with thyrotoxicosis and to share what the task force believes is current, rational, and optimal medical practice.

Hyperthyroidism and other causes of thyrotoxicosis: management guidelines of the American Thyroid Association and American Association of Clinical Endocrinologists

BACKGROUND

Thyrotoxicosis has multiple etiologies, manifestations, and potential therapies. Appropriate treatment requires an accurate diagnosis and is influenced by coexisting medical conditions and patient preference. This article describes evidence-based clinical guidelines for the management of thyrotoxicosis that would be useful to generalist and subspeciality physicians and others providing care for patients with this condition.

METHODS

The development of these guidelines was commissioned by the American Thyroid Association in association with the American Association of Clinical Endocrinologists. The American Thyroid Association and American Association of Clinical Endocrinologists assembled a task force of expert clinicians who authored this report. The task force examined relevant literature using a systematic PubMed search supplemented with additional published materials. An evidence-based medicine approach that incorporated the knowledge and experience of the panel was used to develop the text and a series of specific recommendations. The strength of the recommendations and the quality of evidence supporting each was rated according to the approach recommended by the Grading of Recommendations, Assessment, Development, and Evaluation Group.

RESULTS

Clinical topics addressed include the initial evaluation and management of thyrotoxicosis; management of Graves' hyperthyroidism using radioactive iodine, antithyroid drugs, or surgery; management of toxic multinodular goiter or toxic adenoma using radioactive iodine or surgery; Graves' disease in children, adolescents, or pregnant patients; subclinical hyperthyroidism; hyperthyroidism in patients with Graves' ophthalmopathy; and management of other miscellaneous causes of thyrotoxicosis.

CONCLUSIONS

One hundred evidence-based recommendations were developed to aid in the care of patients with thyrotoxicosis and to share what the task force believes is current, rational, and optimal medical practice.

Familial dysalbuminemic hyperthyroxinemia

A family with familial dysalbuminemic hyperthyroxinemia is described. The syndrome is inherited as an autosomal dominant trait and is characterized by marked elevation of serum thyroxine, due to increased binding of thyroxine to albumin, whereas serum triiodothyronine is normal. Serum free thyroxine is normal when measured with ultrafiltration or equilibrium dialysis, but artefactually high when measured with an analogue assay. The importance of the condition, which is harmless, lies in the misinterpretation of values with subsequent erroneous treatment of thyrotoxicosis. By using an ultrasensitive TSH method it is possible to discriminate between euthyroid and hyperthyroid patients and thereby to avoid incorrect diagnosis in subjects with euthyroid hyperthyroxinemia.

The thyroxine-binding proteins

The slow clearance, prolonged half-life, and high serum concentration of thyroxine (T4) are largely due to strong binding by the principal plasma thyroid hormone-binding proteins, thyroxine-binding globulin (TBG), transthyretin (TTR), and albumin. These proteins, which shield the hydrophobic thyroid hormones from their aqueous environment, buffer a stable free T4 concentration for cell uptake. Free rather than bound T4 is subject to homeostatic control by the hypothalamic-pituitary thyroid axis. Although it is not a protease inhibitor, sequence analysis identifies TBG as a member of the serine protease inhibitor (serpin) family of proteins. Proteolytic cleavage of TBG appears to be a mechanism for site-specific release of T4 independently of homeostatic control. TBG probably facilitates the transport of maternal T4 and iodide to the fetus, although this remains to be proven. High-affinity cellular binding sites for TTR have been described; however, their function and that of choroid plexus synthesis of TTR and transport of T4 into the cerebrospinal fluid remain unclear. Albumin, with the lowest T4 affinity and fastest T4 release of the major T4-binding proteins may promote quick exchange of T4 with tissue sites. The affinity of albumin for T4 is increased by histidine substitution for arginine 218 in the most common form of dysalbuminemic hyperthyroxinemia. However, proline and alanine substitutions at the same site have a similar effect, suggesting that arginine 218 interferes with T4 binding.

A possible new syndrome of familial euthyroid dysproteinemia associated with elevated thyroxine and triiodothyronine

Increased thyroxine (T4) binding to thyroid binding prealbumin (TBPA) or albumin causes a biochemical picture suggestive of thyrotoxicosis with increased total T4 (TT4). Previously described familial syndromes are characterized by increased binding of T4 to thyroid binding globulin (TBG), TBPA, or albumin. Increased T3 binding to TBG has been noted, but we are not aware of any kindreds reported with increased T3 binding to TBPA or albumin. We wish to report a family in which there is increased binding of T3 to TBG, TBPA and albumin. All family members were clinically euthyroid and tested negative for T3 antibodies. This family appears to demonstrate two abnormalities: first, elevated TBG, and second, normal levels of TBPA and albumin with increased binding of T3 and T4 to these proteins. We believe this may represent a new syndrome of familial dysproteinemia in which multiple proteins show enhanced binding of T3 and T4. This could reflect increased binding sites, increased binding affinity, or a combination of both.

A novel variant of transthyretin (prealbumin), Thr119 to Met, associated with increased thyroxine binding

A group of patients with prealbumin associated hyperthyroxinemia possess a common single base substitution in the fourth exon of their transthyretin gene. This cytosine to thymine substitution occurs in the codon for residue 119 and results in the predicted replacement of a threonine residue with a methionine at this position. A new NcoI restriction endonuclease cleavage site is created by the point mutation and can be detected by a rapid and simple assay based on the polymerase chain reaction. This variant transthyretin is inherited in an autosomal dominant manner and is apparently not amyloidogenic but is associated with increased thyroxine binding. As healthy heterozygous individuals have normal serum thyroxine concentrations, the hyperthyroxinemia sometimes found may not be primarily due to the variant.

Variations in thyroid hormone transport proteins and their clinical implications

Variations in major thyroid hormone transport proteins may be inherited or acquired and may be associated with changes in serum concentration of the proteins or their affinity for thyroid hormones. These variations most frequently involve thyroxine-binding globulin (TBG), but changes in transthyretin and albumin are also observed. The consequent alteration of thyroid hormone-binding capacity in serum is associated with variations in total thyroid hormone concentration. Increased serum total thyroid hormone levels are found in subjects with TBG excess, familial dysalbuminemic hyperthyroxinemia, and transthyretin-associated hyperthyroxinemia. Conversely, diminished serum thyroid hormone values are observed in subjects with TBG deficiency, and decreased concentration or affinity of transthyretin and albumin is not associated with variations in serum concentrations of thyroid hormones. The transport protein-associated variations in serum total thyroid hormone concentrations do not reflect a change in thyroid status. Euthyroidism can be easily established in subjects with transport protein abnormalities by the normal free thyroid hormone and TSH concentrations. It is, however, crucial to select methods for free thyroid hormone measurement that are not affected by abnormalities of transport proteins. Some assays, such as the analog method, often provide artifactual and misleading results, which may lead to inappropriate and even detrimental treatments. The evolutionary advantage of TBG (and albumin) in terms of thyroid homeostasis still remains to be elucidated.

A point mutation in transthyretin increases affinity for thyroxine and produces euthyroid hyperthyroxinemia

In a family expressing euthyroid hyperthyroxinemia, an increased association of plasma thyroxine (T4) with transthyretin (TTR) is transmitted by autosomal dominant inheritance and is secondary to a mutant TTR molecule with increased affinity for T4. Eight individuals spanning three generations exhibited the abnormality. Although five of eight individuals had elevated total T4 concentrations, all affected individuals were clinically euthyroid and all had normal free T4 levels. Purified TTR from the propositus had an affinity for 125I-T4 three times that of control TTR. Exons 2, 3, and 4 (representing greater than 97% of the coding sequence) of the TTR gene of DNA prepared from the propositus' peripheral blood leukocytes were amplified using the polymerase chain reaction (PCR) and were sequenced after subcloning. Exons 2 and 3 were indistinguishable from normal. In 50% of clones amplified from exon 4, a substitution of adenine (ACC) for guanine (GCC) in codon 109 resulted in the replacement of threonine-for-alanine, a mutation confirmed by amino acid sequencing of tryptic peptides derived from purified plasma TTR. The adenine-for-guanine substitution abolishes one of two Fnu 4H I restriction sites in exon 4. PCR amplification of exon 4 of TTR and restriction digestion with Fnu 4H I confirmed that five affected family members with increased binding of 125I-T4 to TTR are heterozygous for the threonine 109 substitution that increases the affinity of this abnormal TTR for T4.

In situ localization of transthyretin-mRNA in the adult human liver, choroid plexus and pancreatic islets and in endocrine tumours of the pancreas and gut

In situ hybridization with 35S-labeled single stranded RNA probes was used on sections from formaldehyde-fixed and paraffin-embedded tissue specimens to provide semiquantitative data on the occurrence of transthyretin(TTR)-mRNA in human liver, choroid plexus and pancreatic islets as well as in 15 endocrine tumours of the pancreas and gut. A monoclonal antibody to TTR was used for immunocytochemical identification of the protein in consecutive sections. The amount of TTR-mRNA in hepatocytes was found to be much less than that in epithelial cells of the choroid plexus. Glucagon cells of the pancreatic islets were also specifically labeled and the level of TTR-mRNA in these cells was intermediate between that of hepatocytes and choroid plexus epithelial cells. Four glucagonomas, one malignant insulinoma and two midgut carcinoids were shown to contain TTR-mRNA. The 'in situ' labeled cells were also found to be TTR immunoreactive. These findings present the first conclusive evidence for TTR synthesis in pancreatic islets and in endocrine tumours. They also establish that the high serum concentration of TTR found in some patients with endocrine tumours (notably glucagonomas) is most likely due to tumour production of TTR.

A four generation study of familial dysalbuminemic hyperthyroxinemia: diagnosis in the presence of an acquired excess of thyroxine-binding globulin

We have studied the largest kindred with familial dysalbuminemic hyperthyroxinemia (FDH) thus far reported, comprising thirty-three blood relations in four generations and three of their spouses. Our objective was to complement previous evidence concerning the precise mode of inheritance of FDH and to detect any other features of the disorder that had not yet been noted. Among the thirty three, there were thirteen patients with FDH, eight males and five females, in all of whom the abnormality appeared to be fully expressed. Within the kindred, no affected female has borne a female child, but transmission from female to male, male to male, and male to female has been observed. Among the offspring of individuals with FDH, the overall observed frequency of FDH in three filial generations was 12/22, or 54.5 per cent, yielding a computed penetrance ratio of 1.09. Four of the patients with FDH had been investigated for hyperthyroidism, and two of them had mistakenly been treated. Of particular interest were two women with FDH who were receiving oral contraceptives and whose serum thyroxine-binding globulin (TBG) concentrations were increased. The results of their thyroid function tests differed from those of patients with FDH whose TBG concentrations were normal and mainly suggested the presence of only a high TBG state. The diagnosis of FDH in these two patients was obscured, and probably would not have been made were it not for the present investigation, which led to the electrophoretic demonstration of increased binding of T4 by serum albumin.(ABSTRACT TRUNCATED AT 250 WORDS)